It is known to form containers of the above-described type for use as bottles for cosmetics and pharmaceuticals, for example, utilizing a combined injection and blow molding or combined extrusion and blow-molding technique.
For example in the extrusion-blow-molding method, the parison which is vertically extruded is fed upwardly into a two-part mold which is then closed on the parison. The parison is then expanded by blowing to assume a shape complementary to that of the mold cavity.
The top of the neck is then cut away and the bottle formed in the mold is removed by the opening of the latter in a separation of the two mold parts so that the completed bottle can fall onto a receiving bin or can be deposited on a conveyor which can carry off the bottle from the blow-molding machine.
As will be described in greater detail below, blow-molded bottles formed in this manner generally have a seam extending around the bottle in a plane corresponding to the joint plane or separation plane of the two mold halves. When an attempt is made to imprint such a bottle, the seam tends to interfere with the print rendition so that an apparent defect is created where the print overlies the joint plane.
To avoid this drawback, the bottle may be printed with a positioning recess or other formation which serves to index the bottle in a proper position in the printing machine so that when the print pattern is applied, it need not overlap or extend beyond the joint plane and hence the seam.
Thus it is necessary to provide each bottle with an indexing or positioning formation and generally it is necessary to check the finished product for failure in alignment of the decor with the surfaces of the bottle free from the seams. These requirements complicate both the printing apparatus and the printing process.
Furthermore, plastic bottles fabricated in the above-mentioned manner have relatively limited rigidity and thus tend to deform under action of a printing roller or blanket if one does not apply air under pressure to the interior of the bottle during printing. The need for delivery of compressed air to the bottle complicates the printing apparatus.
Finally, the fact that injection-blow-molding and extrusion-blow-molding processes tend to produce products which do not have a high degree of uniformity in wall thickness must be mentioned.
This, of course, poses a problem not only in printing but with respect to the appearance of the bottle, the filling thereof and the uniformity of strength thereof.